Thermal insulation sheaths having inside volumes that contain ducts are already known, said sheaths being constituted by sleeves of thermally insulating resilient foam material. Such sheaths serve to prevent heat being transmitted via the environment to said ducts, and mainly, when said ducts convey a hot fluid, they prevent heat being radiated by said ducts to the outside thereof. This avoids heat being lost from said hot fluid.
In such known resilient sleeves, a longitudinal join plane is provided as determined by a radial slit. Thus, sheaths can be put into place on ducts, and conversely sheaths can be removed from said ducts, by resiliently separating the lips of said radial slit to enable the ducting for protection to be passed therethrough.
However, with such known sheaths, said radial slit constitutes a weak point in the insulation between said ducts and their environment. Heat can easily pass through such a sheath surrounding ducting even if the slit appears to be closed. In addition, in the event of a fire occurring in said outside environment, the fire or the resulting flames can reach and possibly destroy said ducting (particularly at joints between lengths of ducting) by passing through said slit, even if the material from which the sheath is made stands up well to fire and to flames.
An object of the present invention is to remedy this drawback.